A. Field of the Invention
The present invention relates generally to network data transmission, and more particularly, to data transmission through cable modem systems.
B. Description of Related Art
Cable modems allow end-users to connect to networks, such as the Internet, through cable TV lines. In a manner similar to traditional telephone modems, cable modems modulate between digital signals from an attached computing device to analog signals that are transmitted over the cable lines. Unlike traditional telephone dial-up modems, however, cable modems may provide significantly greater throughput.
Cable modems are generally installed locally to the end-user, and communicate with a cable modem termination system (CMTS) at a local cable TV company office. Multiple cable modems may share a single communication channel with the CMTS. The cable modems can receive signals from and send signals to the CMTS, but not to other cable modems on the channel.
In addition to providing traditional network data to users, cable modems may provide telephony services to users. VoIP (voice over IP—that is, voice delivered using the Internet Protocol) is a term used in IP telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol. In general, VoIP refers to the sending of voice information in digital form in discrete packets rather than using the traditional circuit-committed protocols of the public switched telephone network (PSTN). Through a cable modem, a cable company may provide VoIP services, in addition to traditional network data, to its end-users.
One issue that arises in VoIP is quality of service (QoS). When a user places a telephone call, the user expects that the connection will remain active and contain sufficient bandwidth throughout the telephone call. In other words, it is generally unacceptable for a telephone call to fade in and out during the course of the call. In contrast, users receiving traditional network data through a cable modem may not notice short data interruptions.
Occasionally, a module in the CMTS that communicates with a number of cable modems may fail. The CMTS may handle the failure by bringing a backup module on-line. The backup module takes over the data flows that the original module was handling. Ideally, the rollover to the backup module should occur without affecting communication sessions with the cable modems. In reality, however, some disruption in service will occur.
There is a need in the art to minimize communication session disruptions to cable modem end-users when bringing backup modules in the CMTS on-line. This is particularly true when VoIP services are involved.